The present invention relates to a curable organosiloxane-based composition or, more particularly, to an organosiloxane-based composition curable by the mechanism of addition reaction between silicon-bonded hydrogen atoms and aliphatically unsaturated hydrocarbon groups bonded to the silicon atoms having usefulness as a sealant or coating agent as well as for the preparation of various molded and shaped articles with excellent workability and storability by virtue of the excellent curability by heating at 70.degree. to 150.degree. C. along with good storability at room temperature over a long period of several months or even longer without increase in the consistency or the phenomenon of gelation.
It is well established in the silicone industry that an organopolysiloxane having a plurality of vinyl groups bonded to the silicon atoms and an organohydrogenpolysiloxane having a plurality of hydrogen atoms directly bonded to the silicon atoms jointly pertain to the so-called addition reaction or hydrosilation reaction in the presence of a trace amount of a platinum compound as a catalyst for the reaction so that a composition comprising these ingredients can be cured by forming crosslinks between the polysiloxane molecules. The platinum compound most conventionally used in the above mentioned purpose is chloroplatinic acid in the form of a solution in an alcohol such as isopropyl alcohol, of which at least a part of the ligands to the platinum atom may optionally be modified with an alcohol or replaced with ethylene molecules, or in the form of a complex with a vinyl-containing low-molecular organopolysiloxane. When compounded with an appropriate amount of such a platinum catalyst, the polysiloxane composition can be cured by heating, for example, for around 30 minutes at a temperature of 70.degree. to 150.degree. C.
Since the above mentioned platinum compoubnds each have a very high activity for the hydrosilation reaction between silicon-bonded vinyl groups and silicon-bonded hydrogen atoms, an organopolysiloxane composition comprising a vinyl-containing organopolysiloxane and an organohydrogenpolysiloxane with admixture of a platinum catalyst has a disadvantage that the addition reaction proceeds even at room temperature at a considerably high velocity so that the composition cannot be stored over months due to occurrence of an increase in the consistency or gelation which may take place already within 24 hours at room temperature.
A conventional countermeasure to solve the above mentioned problem of low storability is that the ingredients of the composition are divided in a two-package formulation into two groups forming separate packages, the content in each of which is prolongedly storable, and the contents of the two packages are mixed together immediately before use of the completed composition. Such a two-package formulation is of course disadvantageous because of the troublesomeness of the blending work necessitated before each time of use and the troubles due to an eventual inaccurate mixing proportion or incomplete mixing of the contents of the two packages. Alternatively, the composition is prepared in a one-package formulation but with further admixture of a reaction retarder such as a metal salt of an organic acid and an acetylenic alcohol, e.g., 3-methyl-1-butyn-3-ol, 1-ethynyl-1-cyclohexanol and the like. The addition of a reaction retarder is also undesirable because such a retarder compound is not an inherently essential component of the composition eventually to affect the properties of the composition after curing. Instead of the addition of a reaction retarder, it is proposed that the composition prepared in a one-package formulation is stored at a low temperature of, for example, -20.degree. C. or even lower although this method is, needless to say, far from practicability.